In general, an original signal transmitted by a certain transmitter (hereinafter, simply called a "wanted signal") is always received at a receiving set together with other plural interfering signals. Since the level of distortion in a telecommunication system is determined by the ratio between the power of the wanted signal and total power of all the interfering signals, even if the level of the wanted signal is much higher than each of the interfering signals, the distortion of the communication system can pose a serious problem when the total power of all the interfering signals proportionally increase according to when the number of the interfering signals is rather high. In conventional telecommunication systems, interfering signals make it very difficult to extract the information from the wanted signal.
Although an antenna array system has been considered as a countermeasure to improve the problems caused by the interfering signals, no practical method of synthesizing the antenna array system in an actual telecommunication systems, particularly for mobile communication systems, has yet been suggested. The problems of applying conventional antenna array systems, which is based on the method of Eigen-Decomposition, is mainly due to its complexity and operating speed which is too large for real-time processing in telecommunication systems.
The conventional technique about the antenna array system was introduced in the following references:
[1] M. Kaveh and A. J. Barabell, "The Statistical Performance of the MUSIC and Minimum-Norm Algorithms for Resolving Plane Waves in Noise," IEEE Trans., Acoust., speech and signal process., vol. ASSP-34, pp. 331-341, April 1986. PA1 [2] T. Denidni and G. Y. Delisle, "A Nonlinear Algorithm for Output Power Maximization of an Indoor Adaptive Phased Array," IEEE Electromagnetic Compatibility, vol. 37, no. 2, pp. 201-209, May, 1995. PA1 [3] B. G. Agee, S. V. Schell, and W. A. Gardner, "Spectral Self-Coherence Restoral: A New Approach to Blind Adaptive Signal Extraction Using Antenna Arrays", Proc. of IEEE, Vol. 78, No. 4, pp. 753-767, April 1990. PA1 (a) setting the initial estimation vector v(0) with a predetermined value, setting the initial gain vector w(0) with the normalized estimation vector, i.e., v(0)=x(0) and ##EQU3## PA1 (b) Receiving a new signal vector x(n) at the present snapshoht; PA1 (c) updating the estimation vector v(n) and gain vector w(n) from the new signal vector by v(n)=f v(n-1)+(1-f)x(n)x.sup.H (n)w(n-1) and ##EQU4## PA1 (d) going to the following step (e), for more iteration in the present snapshot, or going to said step (f), for no more iteration in the present snapshot; PA1 (e) going back to said step (c), with v(n-1).rarw.v(n) and w(n-1).rarw.w(n) for more iteration in the present snapshot; PA1 (f) generating the final array output y(n) at the present snapshot by y(n)=w.sup.H (n)x(n), and going back to said step (b), with incremented snapshot index n, i.e., n.rarw.n+1, for continuing the procedure at the next snapshot.
The problems in most conventional methods of designing antenna array systems are, first, it, except the method introduced in [3], requires some knowledge about the location of the wanted signal apriori, and second, it requires so many computations that real-time processing cannot be performed. Especially, when the anival angle of the wanted signal or the total number of signal sources is unknown, the required amount of computation becomes even larger, which makes it impossible to apply the conventional method of synthesizing the antenna array system to practical signal environments, such as mobile communications.
Another undesirable feature of most conventional methods of designing antenna array systems is that the performance and/or the complexity of the system to be built is affected by the coherence and/or cross correlation of the wanted signal with respect to the interfering signals. This means that the antenna array system often requires additional complexities when the signals are fully or partially coherent so that the resultant system becomes too complicated for real-time processing, which is very important, especially in mobile communications. Another conventional methods, such as the one shown in [3], do not work at all if the wanted signal cannot be extracted from the interfering signals with a particular frequency separation at a proper time lag.
This invention introduces a new signal processing technology of designing an antenna array system that provides for a nice beam pattern having its maximum gain along the direction of the wanted signal maintaining the gain along the directions of interfering signals in relatively much lower levels. Under the assumption that the wanted signal is sufficiently larger in magnitude than each of the interfering signals, the proposed technique generates the desired beam pattern without requiring any knowledge about the wanted signal as well as the interfering ones Another important and attractive aspect of the proposed technique is that the total required amount of computation is so small that the optimal parameters of the antenna array system are produced on a real-time basis. In fact, the signal processing apparatus, which forms the beamforming module of the antenna array system introduced in this invention, can easily be implemented with a normal, off the shelf, digital signal processor.
The primary objective of this invention is to introduce a new signal processing method for designing a beamforming module of an antenna array system in order to apply it at the base station of a mobile communication system for receiving and transmitting the signal of each subscriber in a cell with a nice beam pattern which is provided individually for each subscriber of the cell. The proposed technique can also be applied in other signal environments such as WLL(wireless local loop) and other fixed communications as well as mobile communications.